Dendritic growth of ammonium chloride crystals: Measurements of the concentration field and a proposed nucleation model for growth

Abstract

We have developed a method of investigating the solute concentration field around a dendrite growing from a supersaturated ammonium chloride solution. It uses the refractive index of the solution as a measure of its concentration. The spatial dependence of refractive index is measured with the aid of an interference microscope. The field distributions obtained in this way indicate a nonlinear relationship between growth velocity and driving force. We propose a model for dendritic growth based on homogeneous nucleation at a temperature below the surface roughening temperature. We show that it is consistent with the measurements and also provides a mechanism of pattern selection.